Transmitter and method for digital multi-carrier transmission

ABSTRACT

The present invention relates to a transmitter and method employing a multi-carrier transmission method, especially utilizing real coefficient wavelet filter banks. The transmitter includes a preamble data generator, a modulator, and a ramp processor. The preamble data generator generates preamble bit data, and outputs the preamble data. The modulator modulates the preamble data, generates a plurality of subcarriers, and outputs a composite wave of the time waves of the plurality of subcarriers. Subsequently, the ramp processor performs ramp processing on the composite wave with a certain delay period from a reference position of the composite wave.

This is a continuation application of application Ser. No. 10/983,010filed Jul. 2, 2004, which is based on JP 2003-190953 filed Jul. 3, 2003,the entire contents of each of which are incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmitter and transmission methodemploying a multi-carrier transmission technique, particularly a digitalwavelet multi-carrier (DWMC) transmission technique utilizing realcoefficient wavelet filter banks.

2. Description of the Related Art

Orthogonal frequency division multiplexing (OFDM) is frequently adoptedas a conventional multi-carrier transmission method, for example, asdescribed in U.S. Pat. No. 6,442,129. In the OFDM transmission method,discrete Fourier transform (DFT), particularly fast Fourier transform(FFT), is adopted as a modulation/demodulation method. In addition, inFFT-based OFDM, generally speaking, ramp processing is adopted, whichmakes the time waveform on a leading edge of a frame (preamble) smoothin order to prevent the waveform from distorting in a transmissionchannel or in hardware such as an amplifier.

Recently, wavelet-based OFDM has been proposed to replace FFT-based OFDMas a modulation/demodulation method in OFDM transmission becauseFET-based OFDM has basic weaknesses such as poor resistance to narrowband interference, poor resistance to internal interference, and lowtransmission efficiency because of the necessity of a cyclic prefix.When ramp processing is performed in wavelet-based OFDM, the length ofthe preamble data in the wavelet-based OFDM is longer by at least (2k−1)symbols (k is an overlapping factor) than the length of the preambledata in the FFT-based OFDM if the wavelet waveform, as it is, is used asdata of the preamble. The greater the length of the preamble data, themore the redundancy of the data increases. Accordingly, the length ofthe preamble data is required to be as short as possible. While autogain control (AGC) is performed in a receiver by using a waveletwaveform without ramp processing, convergence speed of the AGC becomesan issue because of the complexity of the wavelet waveform.

SUMMARY OF THE INVENTION

The present invention is made in view of the above-mentioned problems.An object of the present invention is to provide a transmitter andtransmission method in the DWMC data transmitting method, which enablesshortening of the length of the preamble data and improves theconvergence speed of the AGO.

According to the invention, a preamble data generator generates preamblebit data, and outputs the preamble data. Next, a modulator modulates thepreamble data, generates a plurality of subcarriers, and outputs acomposite wave of the time waves of the plurality of subcarriers.Subsequently, a ramp processor performs ramp processing on the compositewave with a certain delay period from a reference position of thecomposite wave.

In this way, the invention provides a transmitter and transmittingmethod which enables shortening of the length of the preamble data andimproves the convergence speed of the AGC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a transmitter according to a firstembodiment of the invention;

FIG. 2 is a waveform diagram of preamble data according to a firstembodiment of the invention;

FIG. 3 is a diagram showing an example of ramp processing according to afirst embodiment of the invention;

FIG. 4 is a spectrum diagram showing a relationship between subcarriernumbers and frequencies of sine waves;

FIG. 5 is a waveform diagram of preamble data according to a secondembodiment of the invention;

FIG. 6 is a block diagram of an inverse wavelet transformer in atransmitter according to a third embodiment of the Invention;

FIG. 7 is a block diagram of a prototype filter of an inverse wavelettransformer in a transmitter according to the third embodiment of theinvention;

FIG. 8 is a block diagram of another prototype filter of an inversewavelet transformer in a transmitter according to the third embodimentof the invention;

FIG. 9 is a schematic diagram showing a relationship among symbol dataof preamble data, time waveform of preamble data, and ramp processingwaveform;

FIG. 10 is a waveform diagram showing a wavelet waveform;

FIG. 11 is a waveform diagram showing an example of a transmittedwaveform according to the DWMC transmission method;

FIG. 12 is a spectrum diagram showing an example of a transmittedspectrum according to the DWMC transmission method;

FIG. 13 is a schematic frame diagram showing an example of aconfiguration of a transmitted frame according to the DWMC transmissionmethod;

FIG. 14 is a block diagram of another transmitter according to the firstembodiment of the invention; and

FIG. 15 is a block diagram of a power line communication system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the invention will be described with referenceto FIGS. 1 through 15.

First Embodiment

A first embodiment of the invention generates a digital waveletmulti-carrier (DWMC) transmission signal from a plurality of digitallymodulated waves that are received from real-coefficient filter banks.Low bit rate modulation, such as quadrature phase shift keying (QPSK),quadrature amplitude modulation (QAM) or pulse amplitude modulation(PAM), may be used for modulating each carrier.

A data transmission method according to the DWMC transmission methodwill be described with reference to FIGS. 4 and 10-12.

FIG. 10 illustrates a waveform of a wavelet, and FIG. 11 illustrates aDWMC transmission waveform according to the invention. As shown in FIG.10, each waveform 1001 of the wavelet has an impulse response, andimpulse responses of each of the plurality of waveforms 1001 aretransmitted in an overlapping relationship with each other. As shown inFIG. 11, each transmission symbol 1101 is formed by a time waveform 1102that is a combination of impulse responses for a plurality ofsubcarriers.

In FIG. 12, a transmission frame is formed, for example, by several tensto several hundreds of transmission symbols according to the DWMCtransmission method. This transmission frame includes a symbol for atransmission of an information data and a preamble data such as a symbolfor frame synchronization and a symbol for an equalization. The DWMCtransmission signal 1200 includes a plurality of subcarrier signals1201.

FIG. 13 illustrates a configuration of a DWMC transmission frameaccording to the invention. The DWMC transmission frame 1300 comprisesone or more preamble symbols 1301 that are followed by one or moreinformation symbols 1302. The preamble may be used by a receiver forframe synchronization or equalization.

Next, a transmitter 2000 that is preferably for use in the DWMCtransmission method will be described with reference to FIGS. 1 to 3.

FIG. 1 illustrates a block diagram of a transmitter according to a firstembodiment of the invention. A transmitter 2000 includes a preamble datagenerator 10, a symbol mapper 12, a serial to parallel (S/P)transformer16, a plurality of complex data decomposers 18, an inverse wavelettransformer 20, and a ramp processing circuit 22, all of which arecontrolled by a controller (not shown). The operation of transmitter2000 is described below.

Information data may be input to preamble data generator 10. Preambledata generator 10 generates and outputs preamble data, which is used forcarrier detection, synchronization, and/or equalization in a receiver.The preamble data and information data are combined and modulated forrepresentation by symbols. These symbols are produced by: (1)overlapping the preamble and information data and modulating theoverlapped data as the actual transmitting data, (2) forming thepreamble and information data in a composite configuration andmodulating them together, or (3) separately and simultaneouslymodulating the preamble and information data prior to combining thesymbols into a frame.

Symbol mapper 12 transforms bit data of the preamble data andinformation data into symbol data preferably using a low bit ratemodulation method, such as QPSK, QAM, or PAM. Then, symbol mapper 12maps the symbol data into M/2, where M is the number of subcarriers,complex coordinates and serially outputs the mapped data to S/Ptransformer 16.

S/P transformer 16 transforms the serially received mapped data intoparallel data and outputs all but two of the M parallel data streams tocomplex decomposers 18. Each complex decomposer 18 decomposes theparallel data it receives into a real part, which is the in-phasecomponent, and an imaginary part, which is the quadrature component.Each complex decomposer 18 outputs to inverse wavelet transformer 20 thein-phase component as (2n−1)th inputted data and the quadraturecomponent as (2n)th inputted data, where 1≦n≦(M/2−1), M is a positiveinteger, and subcarrier number is 0 to M−1. In total inverse wavelettransformer 20 receives M subcarrier waveforms identified in FIG. 1 assubcarriers 0 through M−1. In FIG. 1, the (2n−1)th and (2n)th datainputted to inverse wavelet transformer 20 correspond respectively tosubcarriers 1 and 2 for n=1, subcarriers 3 and 4 for n=2, and so on.Both ends of subcarriers, namely subcarriers 0 and M−1 are not used,because these contain much direct current components. Even if used, theend subcarrier is not in orthogonal relationship with the nextsubcarrier.

Inverse wavelet transformer 20 has M real-coefficient wavelet filtersthat are orthogonal with respect to each other. Using these waveletfilters, inverse wavelet transformer 20 performs an inverse wavelettransform on both the real and imaginary components it receives. Rampprocessing circuit 22 receives the data generated by inverse wavelettransform 20 and ramp processes this data with a delay, which may beequivalent to fraction of a symbol period, one symbol period, or severalsymbol periods. The ramp processing is accomplished by multiplying datarepresenting a ramp waveform, such as shown in FIG. 3, by the inversewavelet transformed data, as explained below. Thereafter, the rampprocessed data is output by ramp processing circuit 22.

With reference to FIGS. 2 and 3, the ramp processing of the inversewavelet transform data produced by inverse wavelet transformer 20 willbe explained. Particularly, FIG. 2 illustrates a waveform of inversewavelet-transformed Preamble data according to the first embodiment ofthe invention and FIG. 3 illustrates a ramp processing signal accordingto the first embodiment of the invention.

In general, since a wavelet time-waveform 201 of the wavelet transformeddata localizes and is longer than one symbol length, as shown in FIG. 2,waveform 20′ has a moderate initial amplitude rise. Therefore, in manycases, preamble slot 1 includes few effective data for preamblefunctions.

Ramp processing circuit 22 multiplies inverse wavelet-transform waveform201, produced by inverse wavelet transformer 20, with ramp waveform 301to produce a ramp processed product waveform 202. Accordingly, the rampprocessing is performed on the wavelet transformed data, which is acomposite wave, with a predetermined delay from a reference position ofthe composite wave as shown in FIG. 2. Waveform 202 of the rampprocessed data has zero data for the interval of preamble slot 1.Accordingly, waveform 202 of the ramp processed data substantially hasone symbol offset from the rising edge of time waveform 201 of theinverse wavelet transformed data, as shown in FIG. 2.

As illustrated in FIG. 3, ramp processing waveform 301 has a linearlyand monotonically increasing value in preamble slot 2 that tends tosmooth the amplitude product of this waveform and the waveform producedby inverse wavelet transformer 20. The zero value of waveform 301 inpreamble slot 1 effectively eliminates the first symbol of inversewavelet-transform waveform 201 when waveforms 201 and 301 are multipliedto produce ramp processed waveform 202. Also, the unity value ofwaveform 301 in preamble slots 3-6 effectively reproduces the symbolwaveforms of waveform 201, during preamble periods 3-6, when waveforms201 and 301 are multiplied to produce ramp processed waveform 202.

Accordingly, the structure of transmitter 2000 substantially shortensthe length of the preamble data because a head portion of the preambledata is reduced by one symbol, due to the one-symbol period offset ofthe ramp processing. Moreover, the structure of transmitter 2000 makesit possible to improve the processing speed of an automatic gain control(AGC) in the receiver because the ramp processing smooths the waveletwaveform.

The first embodiment has been described based on a transmitter 2000 thatincludes a symbol mapper 12 that performs QAM and complex decomposers18. However, a symbol mapper performing PAM instead of QAM can be alsoused in the first embodiment, as shown in FIG. 14.

FIG. 14 illustrates a block diagram of another transmitter according tothe first embodiment of the invention. In FIG. 14, transmitter 2000includes a symbol mapper 210 that modulates the preamble data providedby preamble data generator 10 using PAM. Symbol mapper 210 performsalmost the same operation as the combined structures of symbol mapper 12and complex decomposers 19 in FIG. 1, by treating the (2n−1)th and(2n)th subcarriers outputted by S/P transformer 16 as the in-phase andquadrature components, respectively, in inverse wavelet transformer 20.

In the above description of the first embodiment, the symbol intervaloffset is set for one symbol interval from the rising edge of the timewaveform. However, the offset is changeable and can be set for severalsymbol intervals, as necessary. In addition, the period of the rampprocessing is set for one symbol interval in the first embodiment.However, the period is changeable and can be set for several symbolintervals as necessary.

Furthermore, a curved waveform such as a raised cosine curve can beemployed as the ramp waveform instead of the linear waveform illustratedby FIG. 3. The curved waveform makes it possible to set the period ofthe ramp processing to less than one symbol interval because the curvedwaveform will prevent the preamble data from increasing transmissionside lobes when the curved waveform and the preamble data are multipliedtogether by ramp processing circuit 22.

Second Embodiment

A transmitter of the second embodiment basically has the sameconfiguration as the transmitter of the first embodiment. However, theramp processing is different from that employed in the transmitter ofthe first embodiment. This difference will be described in detail withreference to FIGS. 1, 3-5, and 16.

In the present embodiment, preamble data generator 10 normally outputsserial data having values of “O” until instructed by the controller tooutput preamble data. When the instruction is received to outputpreamble data, preamble data generator 10 serially generates a value,such as “1,” over several symbol periods so that each subcarrierproduced by S/P transformer 16 contains a series of this value as itspreamble data.

FIG. 9 illustrates a relationship among symbol data 901 of the Preambledata, a time waveform 902 of the preamble data, and a ramp processingwaveform 903 used for generating a DWMC transmission signal according tothe Invention. In FIG. 9, the same symbol data value of “1” isillustrated as being output by preamble data generator 10 for a periodof time beginning with the fourth preamble period so as to provide eachsubcarrier produced by S/P transformer 16 with a series of 1 values inits preamble data.

In the present embodiment, inverse wavelet-transformer 20 includes awavelet filter 904 having a four-symbol interval length. Accordingly, atime waveform value of the preamble data for preamble slot 1 isgenerated from the first four preamble symbol data values (0, 0, 0, 1),which are inputted to wavelet filter 904. Next, a time waveform value ofthe preamble symbol data for preamble slot 2 is generated from the nextgroup of four preamble symbol data values (0, 0, 1, 1) in the series ofsymbol data, which is inputted to wavelet filter 904. According to thiswaveform generation process, each subsequent group of four data valuesincludes a fourth data value in the sequence of preamble symbol data andthe three preceding data values of the preamble symbol data, which wereincluded in the previous group of four data values. By repeatedlyproducing waveform values in this way, a time waveform 902 of thepreamble data can be obtained, as shown in FIG. 9.

FIG. 4 illustrates the spectrum of a DWMC multi-carrier transmissionsignal, and the relationship between subcarrier numbers and frequenciesof sine waves. For the purpose of simplifying the explanation, it isassumed that there are eight subcarriers in the present embodiment, asshown in FIG. 4. The output of the transmitter 2000 is a composite ofthree sine waves that have frequencies of f1, f2, and f3, respectively,as shown by the solid heavy lines in FIG. 4. The three sine waves havephases, φ1, φ2, and φ3, respectively. Each of the phases, φ1, φ2, andφ3, can take any value ranging from −π to π.

Referring now to FIG. 1, the operation of transmitter 2000 in accordancewith the second embodiment of the invention will be described in greaterdetail. First, symbol mapper 12 transforms a bit value of the preambledata into symbol data by using QAM and maps the symbol data into M/2complex coordinates. The mapped complex data of “exp(jφn)” can beobtained by the operation of the symbol mapper 12. Next, S/P transformer16 transforms the serially inputted mapped complex data into paralleldata and outputs M−2 of the parallel complex data streams to complexdecomposers 18. Each complex decomposer 18 decomposes the parallel datait receives into a real part (cos(φn)) and an imaginary part (sin(φ)).Subsequently, each complex decomposer 18 allots “cos(φn)” and “sin(φn)”to the (2n−1)th and (2n)th subcarrier inputs, respectively, provided toinverse wavelet transformer 20. The output from inverse wavelettransformer 20 is the composite wave of the sine waves of“cos(2πfn·t+φn)”, where “fn” is a frequency of the n-th sine wave and“φn” is a phase of the n-th sine wave.

FIG. 5 illustrates a waveform of preamble data according to a secondembodiment of the invention. A waveform 501 is produced from preambledata comprising the same data value, such as “1”, output by preambledata generator 10 for a series of sequential symbol periods. The waveletfilter length used to produce waveform 501 is determined from theexpression X=2kN, where N is the symbol length and, generally, N=M, whenk (overlapping factor) is equal to “2”. In FIG. 5, the real compositewave 501 is a proper sine waveform in preamble No. 4 (i.e. itcorresponds closely to a true sine wave), the ramp processing is carriedout from the preamble No. 4 using the ramp form of FIG. 3 (i.e., usingramp form 903 of FIG. 9). In other words, waveform 502 illustratescomposite waveform 501 after it has been ramp processed by rampprocessing circuit 22. The ramp processing effectively multipliescomposite waveform 501 by time waveform 903 of the ramp processing dataof FIG. 9.

The above-described structure of the second embodiment makes it possibleto substantially shorten the preamble length, since the frame-headportion of the preamble data can be substantially deleted. It ispreferable to substantially delete (X−1) symbol length as the deletedframe-head position. Where, “X” means the filter length determined bythe expression X=2kN. Furthermore, the above-mentioned configurationmakes it Possible to improve the accuracy of the modulation relative tothat of the transmitter described in the first embodiment, since almostthe entire range of the preamble data is a composite waveform consistingof proper sine waves. Furthermore, because initial phases mapped on thecomplex coordinates by the symbol mapper can be voluntarily provided toeach of the (2n−1)th and (2n)th subcarriers, the above-mentionedconfiguration makes it possible to reduce the instantaneous powerconsumption peak when the phases of the subcarriers are set to eliminatean overlap with each other.

Alternative ways of inserting preamble symbols 1301 into the headportion of frame 1300, illustrated by FIG. 13, may be used as well. Forexample, a time waveform of the preamble data without the frame-headportion may be preliminarily created and stored in a memory (not shown),assuming the same preamble data waveform can always be used. When a needarises, the stored waveform can be inserted into the rising edge of thetime waveform of the information data to produce the composite timewaveform of the frame. Also, the number of symbols deleted from thepreamble data by the ramp processing may be regulated in accordance withthe number of “0” values serially occurring in the preamble data beforethe series of “1” values is begun.

A symbol mapper 210 performing PAM instead of QAM can be also used inthe present embodiment, like the first embodiment.

In addition, as described previously for the present embodiment,preamble data generator 10 generates the preamble data by outputting thesame data value (for example “1”) to each subcarrier for a sequence ofserial symbol intervals. As the sequence of serial symbol intervals islengthened, the present embodiment becomes more effective.Alternatively, the period of ramp processing can be set for less thanone symbol interval.

Third Embodiment

A transmitter of the third embodiment has basically the sameconfiguration as the transmitter of the first embodiment. However, theconfiguration of the inverse wavelet transformer 20 will be described ingreater detail here, with reference to FIGS. 6-8.

FIG. 6 illustrates a block diagram of an inverse wavelet transformer ina transmitter according to a third embodiment of the invention. Inversewavelet transformer 20 includes a fast discrete cosine transformer (type4)40, a prototype filter 42, M up-samplers 44, and M−1 delays 46.Up-samplers 44 multiply the sampling rate of the transmitted waveform byM, and delays 46 delay the transmitted waveform.

FIG. 7 illustrates a block diagram of a prototype filter 42 of theinverse wavelet transformer according to the third embodiment of theinvention. Prototype filter 42 is a polyphase filter that includesmultipliers 62, which hold prototype filter coefficients, and adders 64.A general configuration of a polyphase filter is described in “SignalProcessing With Lapped Transform” by Henrique S. Malvar. The order ofthe prototype filter 42 is 2M in the present embodiment.

An operation of the transmitter that has an above-mentionedconfiguration will now be described. The parallel data outputted fromS/P transformer 16 are received by fast discrete cosine transformer(DCT) 40 in inverse wavelet transformer 20. Fast DCT 40 performs a DCTtransform on the received data and outputs the DCT trans formed data toprototype filter 42. Prototype filter 42 filters the DCT transformeddata and produces outputs of filtered data. Each up-sampler 44 performsan up-sampling on a respective one of the filtered data outputs andoutputs up-sampling data. Finally, the up-sampling data are combined,with the cooperation of delays 46, to transform the parallel data intoserial data and the serial data are outputted as transmitting data. Inthe present embodiment, the modulation is performed though thecooperation of prototype filter 42 and fast DCT 40.

FIG. 8 illustrates a block diagram of another prototype filter of theinverse wavelet transformer according to the third embodiment of theinvention. Prototype filter 80 has basically the same configuration asprototype filter 42 but includes delays 60 for delaying received data byone symbol period. The one symbol period is equal to M sampling periodsin the present embodiment. Prototype filter 80 does not process preambledata but, instead, processes information data. Since the configurationof prototype filter 42 has nearly the same configuration as filter 80, asingle device similar to that of prototype filter 80 having switchablebypass circuits around delays 60 may be used to process both thepreamble data and information data, thereby reducing the amount ofcircuitry relative to a transmitter having both prototype filters 42 and80. Prototype filter 42 has no delay devices 60, as does prototypefilter 80. Therefore, prototype filter 42 induces less latency in theoutputted data than does prototype filter 80. Furthermore, while theorder of the prototype filter 42 is 2M (this means k=1) in the presentembodiment, the time latency can be reduced when the order of theprototype filter 42 is 2kM.

Although a fast DCT is used in the inverse wavelet transformer of thethird embodiment, the same processing will be achieved when a fastdiscrete sine transformer (DST) is used instead of the fast DCT. Thefast DST and fast DCT have basically the same configuration, though afilter coefficient differs between the two. The first through thirdembodiments should not be construed as limiting, but rather merelyillustrating, the invention. The DWMC wavelet waveform transmitterdescribed herein can be used in many applications where a generaldigital multi-carrier transmitter is appropriate, such as situationsrequiring a waveform localized in the time and frequency domains.

For each of the first to third embodiments, it is preferable to performthe ramp processing for one symbol interval or more so as to suppressdistortion in the wavelet waveform and prevent the increase of sidelobes in the amplitude spectrum of the wavelet waveform.

While the invention may be applied to a wide variety of communicationapparatuses for transmitting and receiving signals, it is especiallysuitable for power line communication (PLC) systems that may communicateinformation across a poor transmission path. Deregulation is in progressto allow the use of the band from 2 MHz to 30 MHz for PLC. However,other existing systems (e.g., amateur radios and shortwave broadcasts)use the same band. Since no interference with other existing systems isallowed, ideally, no PLC signals should be transmitted to the portionsof the band used by other existing systems.

Normally, a notch filter is used to reduce the amplitude of signalscommunicated in the portions of the band used by existing systems. Anotch filter providing 30 dB of attenuation is used in HOMEPLUG 1.0released by HOMEPLUG, which is an alliance of PLC businesses in theUnited States. Thus, a possible target for the suppression ofinterference to other existing systems is 30 dB or more.

With a DWMC transmission method, a filter bank is used to limit the bandof each subcarrier, so as to suppress subcarrier signals that overlapthe portion of the band used by existing systems. Therefore, the DWMCtransmission method can achieve a similar attenuation of undesirablesignals to that achieved by a conventional notch filter. The deeper theattenuation provided by a filter of DWMC transmitter 2000, the greaterthe filter length of each of the M filters of the filter bank and thegreater the delay attributable to the filters, since filter delay is atrade-off for the attenuation depth. However it is possible to formattenuation notches of 30 dB or more and suppress the filter delay bylimiting the filter length of a PLC filter bank to 4N, using transmitter2000.

FIG. 15 illustrates a block diagram of a power line communication systemaccording to the invention. As shown in FIG. 15, a PLC system in abuilding 750 includes a power line 801; a conventional network 802, suchas a telephone network, an optical network, or a cable television (CATV)network; a communication apparatus 800 including both transmitter 2000,as described in the first to third embodiments, and a receiver (notshown); an audio visual (AV) apparatus 810, such as a television set, avideo device, a digital video disk (DVD) recorder or player, or a DVcamera; a telecommunication apparatus 820, such as a router, anasymmetric digital subscriber line (ADSL), a very high bit-rate digitalsubscriber line (VDSL), a media converter, or a telephone; adocumentation apparatus 830, such as a printer, a facsimile, or ascanner; a security apparatus 840, such as a camera or an interphone; acomputer 850; and a home electrical apparatus 860, such as an airconditioner, a refrigerator, a washing machine, or a microwave oven.

An operation of the PLC system will now be described. Devices 810-860form a network in cooperation with power line 801 and performbi-directional communication using communication apparatuses 800. ForInternet communication, a connection may be made to the Internet via ahome gateway provided in the building 750 through power line 801.Alternatively, a connection may be made via telecommunication apparatus820 to communicate over conventional network 802. Additionally, aconnection may be made on a wireless basis from a telecommunicationapparatus 820 having a radio function. Since communication apparatus 800performs modulation and demodulation processes using filter banksinvolving M filters, which are orthogonal with respect to each other,the interference with the other existing systems can be suppressed bydisabling subcarriers that overlap the band used by the other existingsystems. Further, since the filter length can be limited to 4N, delaysattributable to the filters can be reduced while achieving anattenuation notch depth of 30 dB or more. Also, the effect of narrowband interferences from the other existing systems can be reduced.

Furthermore, when a notch is to be generated in a certain band,transmitter 2000 may effectively accomplish this by disabling anysubcarrier that overlaps the band. It is therefore possible to complywith regulations in various countries easily and with flexibility. Evenwhen there is a regulation change after the present system is put inuse, the change can be accommodated with flexibility, for example byupgrading the firmware of transmitter 2000.

In addition, the configurations of the first to third embodiments can becombined with each other as needed.

Furthermore, an IC (integrated circuit) chip is used as the preambledata generator 10, the symbol mappers 12 and 112, the serial to parallel(S/P) transformer 16, the complex data decomposer 18, the inversewavelet transformer 20, and the ramp processing circuit 22 of thetransmitter 2000. A FPGA (field programmable gate array) or an ASIC(application specific integrated circuit) is preferably used as the ICchip. Furthermore, it may be possible to use a plurality of IC chips forthe functional blocks such as the preamble data generator 10, the symbolmappers 12 and 112, the serial to parallel (S/P) transformer 16, thecomplex data decomposer 18, the inverse wavelet transformer 20, and theramp processing circuit 22 of the transmitter 2000.

This application is based upon Japanese Patent Application NO.2003-190953 filed on Jul. 3, 2003, the entire technical contents ofwhich are incorporated herein by reference in its entirety.

1. A transmitter employing a digital wavelet multi-carrier modulation,said transmitter comprising: a preamble data generator that generatespreamble bit data and outputs the preamble data; a modulator thatmodulates the preamble data, generates a plurality of subcarriers, andoutputs a composite wave of time waves of the plurality of subcarriers;and a ramp processor that performs ramp processing on the composite wavewith a predetermined delay from a reference position of the compositewave.
 2. The transmitter according to claim 1, wherein saidpredetermined delay is one symbol interval delay or less from thereference position of the composite wave.
 3. The transmitter accordingto claim 1, wherein said predetermined delay is more than one symbolinterval delay from the reference position of the composite wave.
 4. Thetransmitter according to claim 1, wherein the composite wave localizesin time and frequency domain.
 5. A transmitter employing digital waveletmulti-carrier modulation, said transmitter comprising: a preamble datagenerator that generates preamble bit data and outputs the preamble bitdata; a symbol mapper that transforms the preamble bit data to symboldata; a wavelet transformer that performs a wavelet transform of thesymbol data, generates a plurality of subcarriers, and outputs acomposite wave of time waves of the plurality of subcarriers; and a rampprocessor that performs ramp processing on the composite wave with apredetermined delay from a reference position of the composite wave. 6.The transmitter according to claim 5, wherein said preamble datagenerator generates the preamble bit data by giving, for eachsubcarrier, the same bit value in a series of symbol intervals.
 7. Thetransmitter according to claim 5, wherein said ramp processor performsthe ramp processing to the preamble bit data from the first symbolinterval having a proper sine wave.
 8. The transmitter according toclaim 5, wherein said ramp processor performs the ramp processing forone symbol interval or more.
 9. The transmitter according to claim 8□Cwherein said ramp processor performs the ramp processing to the preamblebit data from the first symbol interval having a proper sine wave.
 10. Atransmitter employing digital wavelet multi-carrier modulation, saidtransmitter comprising: a preamble data generator that generatespreamble bit data and outputs the preamble bit data; a symbol mapperthat transforms the preamble bit data into symbol data, maps the symboldata into complex coordinates and outputs mapped data; aserial-to-parallel transformer that transforms the mapped data inputtedserially into parallel data; a complex decomposer that decomposes theparallel data into in-phase component and quadrature component, andoutputs the in-phase component and the quadrature component; a wavelettransformer that comprises M real coefficient wavelet filters which areorthogonal with respect to each other (M being a positive integer) andthat receives the in-phase and quadrature component as (2n−1)th and(2n)th inputted data, respectively, performs a wavelet transform of theinputted data, generates a plurality of subcarriers, and outputs acomposite wave of time waves of the plurality of subcarriers; and a rampprocessor that performs ramp processing on the composite wave with apredetermined delay from a reference position of the composite wave. 11.The transmitter according to claim 10, wherein said inversewavelet-transformer further comprises: a fast discrete cosinetransformer that performs a cosine transform on the inputted data toproduce transformed data; a prototype filter that comprises a realcoefficient polyphase filter, an adder, and a multiplier, and thatfilters the transformed data to produce filtered data; M up-samplersthat perform an up-sampling on the filtered data to produce up-sampleddata; and M−1 delays that delay the up-sampled data by a certain period.12. A transmitter employing digital wavelet multi-carrier modulation,said transmitter comprising: a preamble data generating means forgenerating preamble bit data, and for outputting the preamble data; amodulating means for modulating the preamble data, for generating aplurality of subcarriers, and for outputting a composite wave of thetime waves of the plurality of subcarriers; and a ramp processing meansfor performing ramp processing on the composite wave with apredetermined delay from a reference position of the composite wave. 13.A transmitting method employing digital wavelet multi-carriermodulation, said transmitting method comprising: generating preamble bitdata and outputting the preamble data; modulating the preamble data,generating a plurality of subcarriers, and outputting a composite waveof the time waves of the plurality of subcarriers; and performing rampprocessing on the composite wave with a predetermined delay fromreference position of the composite wave.
 14. The transmitter of claim 1wherein the modulator comprises: a symbol mapper that transforms thepreamble bit data into symbol data and maps the symbol data into M/2complex coordinates, where M is the number of subcarriers; aserial-to-parallel transformer that serially receives the mapped symboldata and transforms the mapped symbol data into parallel data; a complexdecomposer that decomposes the parallel data into real and imaginaryparts; and an inverse wavelet transformer comprising M real-coefficientorthogonal wavelet filters that cooperate to inverse wavelet transformboth the real and imaginary parts into the composite wave.
 15. Thetransmitter of claim 1, wherein the modulator comprises: a symbol mapperthat modulates the preamble bit data to produce symbol data and maps thesymbol data into M/2 complex coordinates, where M is the number ofsubcarriers; a serial-to-parallel transformer that serially receives themapped symbol data and transforms the mapped symbol data into paralleldata; and an inverse wavelet transformer comprising M real-coefficientorthogonal wavelet filters that cooperate to decompose the parallel datainto real and imaginary parts and inverse wavelet transform both thereal and imaginary parts into the composite wave.
 16. The transmitter ofclaim 1S, wherein the inverse wavelet transformer comprises: atransformer comprising one of a discrete cosine transformer (DCT) and adiscrete sine transformer (DST) that DCT or DST transforms the real andimaginary parts to produce transformed data; up-samplers that eachup-sample components of the transformed data after the components of thetransformed data are each respectively filtered by a separate one of theM real-coefficient orthogonal wavelet filters; and a combining devicethat combines all of the up-sampled components into the composite wave.17. The transmitter of claim 15, wherein the M real-coefficientorthogonal wavelet filters cooperate as a polyphase filter with an orderof 2M.
 18. The transmitter of claim 15, wherein the M real-coefficientorthogonal wavelet filters cooperate as a polyphase filter with an ordergreater than 2M.
 19. The transmitter of claim 15, wherein: the Mreal-coefficient orthogonal wavelet filters comprise filter banks of alength four times the symbol length that cooperate as a polyphasefilter; and the coefficient values of the M filter banks are selectivelycontrollable to attenuate spectral components of the composite wavefalling within a frequency range by 30 decibels.
 20. The transmitter ofclaim 1, wherein the ramp processing comprises combining the compositewave with a linearly and monotonically increasing waveform to produce asmoothed waveform.
 21. The transmitter of claim 1, wherein the rampprocessing comprises combining the composite wave with a raised cosinewaveform to produce a smoothed waveform.
 22. A transmitter employing adigital wavelet multi-carrier modulation, said transmitter comprising: apreamble data generator that generates preamble bit data, and outputsthe preamble data; a symbol mapper that transforms the preamble data tosymbol data; a wavelet transformer that performs a wavelet transform ofthe symbol data, generates a plurality of subcarriers, and outputs acomposite wave of the plurality of subcarriers; and a ramp processorthat performs ramp processing on the composite wave with a predetermineddelay.
 23. A transmitter employing a digital wavelet multi-carriermodulation, said transmitter comprising: a preamble data generator thatgenerates preamble bit data, and outputs the preamble data; a symbolmapper that transforms the preamble data to symbol data; a wavelettransformer that performs a wavelet transform of the symbol data,generates a plurality of subcarriers, and outputs a composite wave ofthe plurality of subcarriers; and a ramp processor that performs rampprocessing on the composite wave with a predetermined delay.